The breakdown of the \(N=20\)  shell closure has been discussed extensively in Ref. [1]}, [2]}, [3]}
and is associated with the emergence of deformation [4]}, [5]}, [6]},
the natural shell evolution due to tensor forces [7]}, [8]}, and weak binding.
The rearrangement of the single-particle structure in this region [9]}, [10]}, [11]}, [12]} favors a strong mixing
of the positive-parity \(sd\)  shells with negative-parity \(fp\)  shells or intruder shells,
leading to parity inversions in the ground states of several nuclei as compared to the standard shell model predictions.
Such nuclei, in which intruder configuration dominate the ground state, form the so-called island of inversion (IOI).
In recent years, with the development of experimental technology, the boundaries of the IOI have been greatly expanded.
Some nuclei, such as \(^{28,29}\) F [13]}, [14]}, \(^{28}\) Ne [15]}, \(^{29,30}\) Na [16]}, [17]}, [18]}, [19]},
and \(^{31,35,36}\) Mg [20]}, [21]}, [22]}, have all been experimentally confirmed as part of the IOI.
